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* Added an experimental feature suggested by Andres: ellipses ("...")

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in attribute set pattern matches.  This allows defining a function
  that takes *at least* the listed attributes, while ignoring
  additional attributes.  For instance,

    {stdenv, fetchurl, fuse, ...}:
    
    stdenv.mkDerivation {
      ...
    };
    
  defines a function that requires an attribute set that contains the 
  specified attributes but ignores others.  The main advantage is that
  we can then write in all-packages.nix

    aefs = import ../bla/aefs pkgs;

  instead of

    aefs = import ../bla/aefs {
      inherit stdenv fetchurl fuse;
    };

  This saves a lot of typing (not to mention not having to update
  all-packages.nix with purely mechanical changes).  It saves as much
  typing as the "args: with args;" style, but has the advantage that
  the function arguments are properly declared (not implicit in what
  the body of the "with" uses).
This commit is contained in:
Eelco Dolstra 2008-08-14 14:00:44 +00:00
parent db4f4a8425
commit 9279174dde
14 changed files with 57 additions and 23 deletions
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12
src/libexpr/eval.cc
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@ -84,11 +84,12 @@ static void patternMatch(EvalState & state,
ATerm name;
ATermList formals;
Pattern pat1, pat2;
ATermBool ellipsis;
if (matchVarPat(pat, name))
subs.set(name, arg);
else if (matchAttrsPat(pat, formals)) {
else if (matchAttrsPat(pat, formals, ellipsis)) {
arg = evalExpr(state, arg);
@ -122,8 +123,8 @@ static void patternMatch(EvalState & state,
}
/* Check that each actual argument is listed as a formal
argument. */
if (attrsUsed != nrAttrs)
argument (unless the attribute match specifies a `...'). */
if (ellipsis == eFalse && attrsUsed != nrAttrs)
throw TypeError(format("the function does not expect an argument named `%1%'")
% aterm2String(attrs.begin()->key));
}
@ -402,9 +403,10 @@ Expr autoCallFunction(Expr e, const ATermMap & args)
Pattern pat;
ATerm body, pos;
ATermList formals;
ATermBool ellipsis;
/* !!! this should be more general */
if (matchFunction(e, pat, body, pos) && matchAttrsPat(pat, formals)) {
if (matchFunction(e, pat, body, pos) && matchAttrsPat(pat, formals, ellipsis)) {
ATermMap actualArgs(ATgetLength(formals));
for (ATermIterator i(formals); i; ++i) {